1. Field of the Invention
The present invention relates to an electrically data-rewritable nonvolatile semiconductor memory device and a method of data read therein.
2. Description of the Related Art
As miniaturization technology approaches its limit, much is expected from stacking of memory cells as a way of improving bit density in nonvolatile semiconductor memory devices such as NAND flash memory. As an example, there is proposed a stacking-type NAND flash memory configured by a memory cell using a vertical-type transistor (refer to, for example, Japanese Unexamined Patent Application Publication No. 2007-266143). Operation, including a read operation, of the stacking-type NAND flash memory is substantially the same as operation of a conventional planar-type NAND flash memory. Consequently, when attempting to increase a capacity of the stacking-type NAND flash memory, it is important that, during read, a leak current from a non-selected memory string which is not subject to the read operation is curbed.
Conventionally, a NAND flash memory curbs the leak current from a non-selected memory string by applying a ground potential or a negative potential to a gate of a select transistor connected to the non-selected memory string. Moreover, conventionally, a NAND flash memory solves the above-described problem by decreasing a number of memory strings connected to one bit line. In recent years, there is a need to further increase curbing of the leak current, in addition to the conventional technology.